Psychologists measure a child's IQ, or intelligence quotient, by using tests such as the WISC IQ test, which stands for Wechsler Intelligence Scale for Children. The Wechsler test is the most frequently used and there are different variations of the test based on age groups. The WISC-IV, for example, is used to test children from the age of 6 to 16. The WAIS-IV is for testing children who are 16 up to 89 years of age. These tests measure factual knowledge, abstract reasoning, short-term memory, simple logic and visual-spatial abilities.

Obtain a copy of a WISC-IV IQ test. You can purchase them online complete with scoring and interpretation instructions; however, intelligence tests are meant to be administered to children by trained professionals. Alternatively, you can ask for the WISC-IV to be administered to your child through his school if you have a reason to believe that your child may have an unusual IQ score.

Ask the child the questions on the WISC test. A question might, for example, ask the child to describe how two different object are alike. The child may have to do a simple math equation without using paper or give an oral definition of a word. Another type of question is asking the child to repeat a series of dictated numbers, first forward and then backwards.

Calculate the IQ test results. The intelligence quotient was first used by French psychologist Alfred Binet. The "quotient" part refers to his definition of IQ formula. You need to calculate the child's mental age by dividing it by the child's chronological age. You then multiply that number by 100, which will result in a whole number. For example, if an 8 year old child has the mental ability of a 12-year old child, then it is one and a half times his chronological age. The math quotient would be 12 divided by 8 equals 1.5. When this number is multiplied by 100, then the child's ratio IQ is 150. Any child that is functioning at the average level for his age would score an intelligence quotient of 100.

Score each section. Once you have administered the test, you need to score each section, such as verbal or math ability. Depending on how well the child did with her response, you will assign a number score for that section. Add up all the scores for each section to determine the overall IQ score.

Compare the results of the child's overall IQ. An extremely low score of 10 would indicate profound developmental delays, and there would be fewer than one out of 100,000 children with a score this low. A score of 70 would be considered borderline-delayed and, typically, two out of 100 children would achieve this score. Half of children taking the WISC IQ test will score 100, which is the average score. A score of 125 would indicate superior intelligence and a score of 130 means the child is very gifted -- a genius.